In the past years, significant efforts have been devoted to develop processes for the production of pulp and paper products aimed at reducing manufacturing costs while improving product quality. Quality control of the raw materials entering in the production of pulp and paper products, particularly regarding wood chips used, has been identified as a key factor in process optimization.
A known approach to control quality of wood chips consists in treating wood chips at the manufacturing stage. Such an approach is employed in the wood chips manufacturing method disclosed in U.S. Pat. No. 5,577,671 issued on Nov. 26, 1996 to Seppanen et al, which method consists of separating from ground whole-tree chips, bark and cellulose wood chips through a series of separation stages including pneumatic separation, vibration segregation with sieve and color difference sorting. The resulting low bark, pale wood chips can be then processed using a minimum quantity of bleaching agent. Although processing cost can be minimized accordingly, added manufacturing cost due to bark separation step may still maintain overall production cost high.
Another known approach consists of sorting trees according to their types prior to wood chips manufacturing, to produce corresponding batches of wood chips presenting desired characteristics associated with these types. Typically, hardwood trees such as poplar, birch and maple are known to generally produce pale wood chips while conifers such as pine, fir and spruce are known to generally yield darker wood chips. In practice, wood chips batches can either be produced from trees of a same type or from a blend of wood chips made from trees of plural types, preferably of a common category, i.e., hardwood trees or conifers, to seek wood chips uniformity. However, chips characteristics basically depending on initial bark content of wood chips used, knowledge of the types of wood chips for a given batch does not necessarily give a reliable indication of the chips quality.